Information retrieval systems are systems that quickly retrieve information suitable for a user's need from a database in which information or data predicted to be required by a user are previously collected, processed and handled and are accumulated in a shape in which the information or data can be easily found and that provide the information to the user.
Information retrieval systems are classified into reference retrieval, fact retrieval, and full-text retrieval according to types of information accumulated in the database. Reference retrieval is to retrieve bibliographic record of a document that mainly handles a subject to be found by a user, and online information retrieval systems, such as DIRLOG, BRS, and the like, correspond to reference retrieval. Fact retrieval is to retrieve general data, numerical data and fact data, and chemical abstracts service on-line (CAS), whereby chemicals are retrieved, electronic information service (EMIS), whereby data of a semiconductor material are retrieved, and the like, belong to the category of fact retrieval. Full-text retrieval is to retrieve bibliographic data, a corresponding text or all of an original text from a database in which a full-text of a document is accumulated, as needed. LEXIS or WESTLAW in which law information can be retrieved, NEXIS in which paper articles can be retrieved, Dow Jones Retrieval, and the like, belong to the category of full-text retrieval.
Large-capacity computing resources are required for a logic operation used to retrieve a keyword from a full-text-based database. However, computing resources that may be used in a mobile environment are limited such that the speed of retrieval is decreased when the logic operation is performed.
Thus, in a full-text-based retrieval system on a mobile terminal, the usage number of logic operators provided is very limited such that effective keyword retrieval cannot be provided.